The present invention relates to an electric hand machine tool, particularly an angle grinding machine.
In particular, the present invention relates to an electric hand machine tool which has a motor casing containing an electric drive with a gear head projecting from one end face of the casing and carrying a tool mounting, and a handle extending from the other end face of the casing and containing an ergonomically situated switch bar for switching on the electric drive.
Hand machine tools, paricularly angle grinding machines, of the above mentioned type are at the present time equipped exclusively with an on/off switch operated by means of a switch bar. The switch bar is situated on the underside of the handle and is operated by at least one finger, while the handle is gripped, and held in the operating position during working with the machine. The ergonomic design of the handle, such as its cross-sectional shape and angle of inclination to the axis of the machine, is optimised for a single working position of the machine. The same also applies to the arrangement of the switch bar, which is often provided with a switch interlock and a switch lock which can be rapidly and reliably operated in this working position.
Some hand machine tools are used in more than one working position for various operations. An angle grinding machine, for example, is used not only for grinding or scouring but also for cutting, for example cutting stone slabs. The optimum working position discussed above is usually provided for the scouring working position in which the grinding wheel points downwards, that is to say lies approximately parallel to the switch bar. In cutting work, on the other hand, the angle grinding machine is turned 90.degree. to the left or right about its longitudinal axis, so that the cutting wheel is approximately at right angles to the workpiece. As a result of this rotation, the handle and switch bar are brought into an unfavourable position relative to the hand gripping the handle. If the machine is turned to the left and the handle is gripped by the right hand, the switch bar comes to lie in the ball of the thumb. If the machine is turned to the right and held by the right hand, the switch bar can be held and operated only by the thumb. In neither case is secure, untiring holding of the switch bar possible. In addition, in the event of danger the position of the switch interlock and switch lock prevents sufficiently rapid reaction and switching-off.
In order to obviate the above mentioned disadvantages, in one known angle grinding machine the gear head and tool mounting for the grinding and cutting wheel are mounted detachably on the motor casing. After unscrewing four fastening screws and removing them from the screw holes, the gear head can be turned 90.degree. to the right or left on the motor casing centring device. The screws then have to be re-inserted and the gear head screwed fast to the motor casing. The dismantling and refitting of the gear head on the motor casing is relatively laborious, so that this known angle grinding machine is not suitable for applications in which adjustments have to be made frequently.